Consensus guidelines on implantable cardioverter-defibrillator (ICD) implantation for primary and secondary prevention of sudden cardiac death are well established and have evolved over the past few years.(1,2) Conversely, internationally agreed, consensus guidelines on ICD programming have hitherto been largely non-existent, despite the effectiveness and risks of ICD therapy being largely dependent on device programming. The 2015 HRS/EHRA/APHRS/SOLAECE guidelines, developed as a collaborative effort between the four continental electrophysiological societies, are the first international guidelines that make comprehensive consensus recommendations on ICD programming.(3) The guidelines address programming of bradycardia algorithms in the context of ICD therapy, tachycardia detection, tachycardia therapy, and intraprocedural testing of defibrillation efficacy. This editorial summarises some of the key recommendations and observations made in these guidelines.(3)

Bradycardia mode and rate programming in the context of ICD therapy

The guidelines for bradycardia programming are largely extrapolated from pacemaker trials and largely similar to bradycardia pacing guidelines. Dual chamber ICDs are recommended for patients with concomitant traditional indications for pacing. Ventricular stimulation must be minimised in both single- and dual-chamber ICDs to reduce the risks of pacemaker syndrome, as well as atrial fibrillation and its sequelae. Given that ICD patients usually do not require bradycardia support, with the exception of patients who require cardiac resynchronisation, the authors stress the importance of avoiding pacing where possible, and in particular ventricular pacing.

In patients with permanent AF, rate adaptive pacing should be the first choice of pacing mode. The committee suggests that the minimum rate can be programmed higher (eg 70bpm) in patients with AF in an attempt to compensate for the loss of active atrial filling, with a restrictive maximum sensor rate to prevent overpacing. AAI or DDD modes are preferable in patients with intact atrioventricular conduction. While unnecessary RV pacing should be minimised by using specific algorithms such as managed ventricular pacing or longer AV delays, this is of greatest importance for patients at higher risk of AF or poorer LV function. As expected, excessively long AV delays that result in non-physiologic AV contraction patterns should be avoided.

In CRT-D patients, consistent delivery of ventricular pacing and CRT optimisation are recommended similarly to that for CRT-P.

Tachycardia detection programming

Here, the authors discuss the problems with initial scepticism regarding the effectiveness of sudden death prevention with ICDs, concern regarding undersensing of VF, increasing defibrillation threshold with the duration of VF, all of which had created a culture of programming for rapid tachycardia detection and the shortest possible time to initial therapy. With the increase in use of ICDs for primary prevention, so did the incidence of avoidable shocks. In addition to physical and psychological distress, it is important to recognise that ICD shocks are associated with higher morbidity. Despite aborting sudden cardiac death, the authors also emphasise that both appropriate and inappropriate ICD shocks have been associated with a considerable increase in the risk of mortality in several studies. This is more likely to be because ICD shocks are a marker of more advanced heart disease and subsequent death, as opposed to a causal relationship. Avoidable shocks could be reduced by appropriately programming the detection rate, detection duration, antitachycardia pacing (ATP), algorithms that differentiate supraventricular tachycardias from VT, and specific programming to minimise noise detection. Reasonably extending detection times can reduce shocks without increasing morbidity or mortality. For both primary and secondary prevention ICD patients, it is recommended that detection duration criteria should be programmed to require the tachycardia to continue for at least 6-12 seconds or for at least 30 intervals before completing detection, to reduce therapies.(3)

The rate cut off for detecting ventricular arrhythmia is a trade-off between maximising sensitivity for ventricular arrhythmias and discriminating fast supraventricular tachyarrhythmias. Whilst in early secondary prevention ICDs, a rate cut-off slightly below the observed VT was thought to be appropriate, relying on rate cut-offs can lead to inappropriate therapies, particularly in primary prevention ICDs. Dual zone programming for detection can be useful to reduce avoidable or inappropriate shocks compared with single zone programming. For primary prevention ICD patients, it is recommended that the slowest tachycardia therapy zone limit should be programmed at 185-200bpm to reduce total therapies. It is also recommended that higher minimum rates for detection might be appropriate for young patients.

It is also recommended that SVT-VT discrimination algorithms should be programmed to include rhythms with rates faster than 200bpm and potentially up to 230bpm to reduce inappropriate therapies. Other options discussed include activating algorithms such as lead ‘noise’ algorithms and T-wave oversensing algorithms to reduce inappropriate therapies.

Subcutaneous ICD (S-ICD)

Candidates for S-ICD must be initially screened with a modified tri-channel surface ECG that mimics the sensing vectors of the S-ICD system. Here, it is advised that it is reasonable to program two tachycardia detection zones: 1 zone with tachycardia discrimination algorithms from a rate below 200bpm, and a second zone without tachycardia discrimination algorithms at rates above 230bpm.

Tachycardia therapy programming

Antitachycardia therapy (ATP) is effective at terminating slow and fast VT with very low rates of adverse events. Up to 2 ATP attempts are recommended based on current data, as additional attempts yield very little additional efficacy. Except when ATP has been documented to be ineffective or proarrhythmic for an individual patient, it is recommended that ATP should be active for all ventricular tachyarrhythmia zones up to 230bpm, and programmed to deliver at least 1 ATP attempt with a minimum of 8 stimuli and a cycle length of 84-88% of the tachycardia cycle length. The authors recommend burst ATP therapy in preference to ramp ATP therapy, to improve the termination rate. It is reasonable to have the ability to activate shock therapy in all ventricular tachyarrhythmia therapy zones, although haemodynamically stable slow VT can be treated without a backup shock.

Defibrillation threshold testing at implantation

Testing defibrillation efficacy has been considered an integral part of ICD implantation for many years, however there is an associated morbidity and wide variability in practice. The guidelines recommend that it is reasonable to omit defibrillation efficacy testing in patients undergoing initial left pectoral transvenous ICD implantation procedures in which appropriate sensing, pacing, and impedance values are obtained with fluoroscopically well positioned RV leads. Furthermore, defibrillation efficacy testing at the time of implantation of a transvenous ICD should not be performed on patients with a documented cardiac thrombus, AF or atrial flutter in the absence of adequate anticoagulation, recent CVA, unstable coronary artery disease, amongst other factors. Defibrillation efficacy testing is, however, recommended in patients undergoing S-ICD implantation.(3)

Conclusion

The 2015 guidelines provide a comprehensive overview of the current state of evidence on ICD programming, acknowledges where the evidence is poor or controversial, and provides appropriate recommendations. It is a long overdue effort that attempts to provide consistent guidance on optimally managing patients with these devices.

References

1. Priori SG, Blomström-Lundqvist C, Mazzanti A, Blom N, Borggrefe M, Camm J, et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: The Task Force for the Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death of the Europe. Eur Heart J. 2015 Nov 1;36(41):2793–867.